i'm going to say it's open to all ages for now, as long as there's an explanation for why they're leaving their parents (if they have a homelife).

the technology that the Alliance has involves interdimensional travel which would allow for timeline skips, dimension skips, universe skips, etc. inspiration for this would be from interstellar if you've seen that. if not, basically think wormholes and black holes affecting the space-time continuum.